At present, most communication power supplies adopt multiple rectifiers connected in parallel for load sharing. Efficiency characteristics of a rectifier may vary with a load. In general, efficiency for a light load may be low, and therefore some rectifiers have to be turned off to optimize system efficiency, such that system may have energy saving effect. In general, a battery may be hooked to an output of a system with multiple rectifiers connected in parallel. An existing efficient energy saving mode is as shown in FIG. 1. A system Micro Control Unit (MCU) controller 17 may be powered by a battery 15. The MCU controller 17 may make a logic decision according to a system load and a single-rectifier efficiency curve, and control some control pins of a secondary power supply 16 by optocoupler isolation, such that the secondary power supply idles. The secondary power supply 16 may serve to provide a DC stabilized voltage to a controlling circuit, a logic circuit, a fan circuit, or the like. Thus, by controlling the secondary power supply to stay idle, a rectifier in an energy saving state may be made to be merely hooked to an AC grid without drawing energy from the grid, thereby achieving better energy saving effect. In FIG. 1, EMI 11 may represent an Electro-Magnetic Interference filter, PFC 13 may represent a Power Factor Corrector.
A communication power supply adopts an AC input. When an AC input produces a long-term high voltage or when a neutral line in a Three-phase Power Supply System is disconnected, although there is no power output in overvoltage protection, an input circuit thereof is still connected to a grid. Without measure-taking at the power supply or the system, an output filtering electrolytic capacitor, generally 450V/470 μF, behind a rectifier bridge, will be damaged. The electrolytic capacitor may then burst, or even a fire at the power supply and a severe failure may be caused, leading to system communication interruption. Therefore, at present high-voltage protection is often implemented via protection at a power supply per se. High-voltage protection at a power supply may further include hiccup protection using a voltage-dividing resistor and hiccup protection via input cutoff with a relay.
A circuit for hiccup protection using a voltage-dividing resistor, as shown in FIG. 2, basically operates as follows. When it is detected that everything is normal, regular relays K1, K2 are closed, in which case contact closure at a primary relay K1 leads to normal power output. When a voltage on an electrolytic capacitor C3 is detected to exceed a set value for high-voltage protection, a primary power circuit stops operating. At the same time the circuit is disconnected at regular relays K1, K2, in which case R2, R1 may be connected in series in the input circuit. Voltage-division may be implemented by impedance variability of R2, such that the voltage on the electrolytic capacitor C3 will not be overly high, implementing high-voltage protection. The R1 in general may be of a fixed resistance. The R2 in general may be a thermistor with a positive temperature coefficient. For a high-voltage protection by voltage division circuit, when an MCU controller issues an energy saving instruction to implement energy saving at a rectifier by controlling a secondary power supply to stop operating, the regular relays K1, K2 lose power rendering circuit disconnection at K1, K2, and R1, R2 are thus connected in series into the circuit. In this case, with a high grid voltage, a high distorted grid harmonic component, or a high environment temperature, R2 also will share a high voltage, thus a low voltage on the electrolytic capacitor C3. Now as the MCU controller issue a rebound-from-energy-saving instruction, the secondary power supply cannot operate right away, and therefore a rectifier cannot rebound right away from energy saving. In FIG. 2, L may represent a live line, N may represent a neutral line, and VD1 may represent a rectifier bridge.
A circuit for hiccup protection via input cutoff with a relay, as shown in FIG. 3, basically operates as follows. When it is detected that everything is normal, a regular relay K1 is closed. In high-voltage protection, the circuit is disconnected at the regular relay K1, an alternative relay K2 is closed. High-voltage protection is implemented by switching K2 with a voltage threshold of a control logic. A device for high-voltage protection by cutoff implements ultra-low standby power consumption by controlling a secondary power supply, during which reliable high-voltage protection may not be guaranteed in an abnormal grid, unless an additional secondary power supply powered by a system battery is provided, which may further complicates the circuit and raise a cost thereof.